Patent GB-115563-A (GB)
Title: Improvements in Control Systems for Electric Motors.
IPC: B60L7/12
Filed: 1917-08-30
Abstract: 115,563. British Westinghouse Electric & Manufacturing Co., (Westing- house Electric & Manufacturing Co.). Aug. 30, 1917. Systems for continuous-current motors only.- In a regenerative system of control for electric motors, the field excitation is compounded by an apparatus which, on a variation in the regenerated current, produces an over-compensated effect which is afterwards reduced by a device acting more slowly than the over-compensating apparatus. The traction motor armatures A<1>, A<2>, with their resistances 18, 19 are connected in parallel for regenerative running and the field coil F<1> is connected with the generating armature 3 of a motor generator 2, 3 across the resistance 18 while the field coil F<2> is similarly connected across the resistance 19. The regenerated currents and the exciting currents from the armature 3 traverse the resistances 18, 19 in the same direction. A shunt circuit from the trolly includes exciting coils 5, 10 on the motor and generator parts of the auxiliary machines, and the coil 5 is opposed by a coil 22 carrying the regenerated current. The values of the resistances 18, 19 are chosen so as to impart a steep speed current characteristic to the regenerating machines. If a sudden alteration occurs in the supply voltage, the excitation of the field coils F<1>, F<2> due to the current from the armature 3 is varied, and, owing to the steepness of the characteristic, this variation is more than sufficient to compensate for the fluctuation of the supply voltage, but this over-compensation is counteracted after a short time interval by the field coil 22 which changes the effective excitation of the armature 2, thereby altering the speed of the motor generator. The motor 2 may have series and shunt field coils and the generator 3 may have a series field coil with a variable number of turns, thus rendering the resistance 38 unnecessary. The field coil for the generator 3 may be arranged to carry both the currents passing through the armatures 2, 3, and the shunt field circuit of the motor 2 may include a variable resistance. Connexions are shown in Fig. 6 for an automatic system of regenerative control of a motor A<1> with a field coil F<1>, a series resistance 81 varied by a controller 82 operated pneumatically subject to control by electro-magnetically actuated valves 96, 97, limit switches 84<h>, 84<e> to operate at high and low current values, and a relay 86 which comes into use during coasting operations. A three-position relay 85 has two operating coils 104, 103 which carry the supply circuit voltage and the voltage generated by the armature A<1> respectively. The valves 96, 97 are operated by coils O<1>, O<2>, the former 96 admitting pressure to the cylinder 94 when its coil O<1> is energized and the latter 97 admitting pressure to the cylinder 95 when its coil O<2> is de-energized. The coil 0' is supplied from the battery through the contacts of the relay 86 and the limit switch 84h, while the coil O<2> is supplied through the contacts of the limit switch 84<e>. The auxiliary generator 3, its series field 80, and the field F<1> of the traction motor are connected across the resistance 81. The switch 154 is controlled from the master controller and is closed during regenerative working but opened during a period of coasting. The amount of resistance 81 in circuit is varied automatically by the controller 82 subject to the actions, of the limit switches 84h, 84<e> and the relays 85, 86. If the supply voltage decreases during coasting, the coil 103 of the relay 85 predominates over the coil 104 and moves the arm to the left to energize the relay 86. This relay rises to break the circuit of the coil O<1> and the controller 82 is rotated until the voltage balance on the relay 85 is restored. The fieldmagnet structures of the auxiliary machines 2, 3 are designed so that the magnets of the motor 2 are more saturated than those of the generator 3 so that a steep speed torque characteristic is obtained. In a modification, the system shown in Fig. 6 is adapted for two motors, the armatures being connected in two parallel circuits each of which includes a fixed resistance. Each motor field winding, with an adjustable resistance and the auxiliary generator, is connected across one of the fixed resistances. The actuating winding of a limit switch may be connected across an inductive winding in the main circuit. In another modification, the auxiliary motor 2 has a field winding carrying the regenerated current which acts to assist the field winding C. A switch is provided to disconnect the additional winding as desired. Or, both field structures of the motor generator may have field coils carrying the regenerated current and arranged differentially with regard to the field coils 5, 10 As shown in Fig. 11, the auxiliary generator 3 may have a field coil 178 acting to assist the coil 10 and shunted across a variable part of the resistance or impedance 176 in the main circuit. When the regenerated current varies, the over-compensation produced bv the immediate variation of current in the field coil F<2> is modified by the variation produced in the coil 178, but this only occurs after a certain lapse of time on account of the high self-induction of the coil 178. As the vehicle speed decreases, the switches 177 are closed to cut out resistance and the coil 178 becomes inoperative at low speeds. The field coil 178 may be connected in the lead 184 and be shunted by a variable resistance, or it may be shunted across the armature 3. A dynamotor with various field arrangements may be used instead of a motor-generator. In the form shown in Fig. 14, a transformer is also introduced. The primary winding 211 carries the regenerated current and the secondary winding 212 carries the current of the generator winding 192 of the dynamotor. The windings are arranged so that the magnetizing effects are opposite in direction. In the system shown in Fig. 16, the rapid over-compensation is produced by a differential field winding on the main motor, one part F<a> of which is included in the regenerating circuit and the other part F<b> is included in the current of the auxiliary generator 3. The shunt field winding 6 is added to the motor 2 to saturate its field and the over-compensation produced by the differential winding F<a>, F<b> is neutralized after a time by the automatic adjustment of the motor-generator set to the new voltage conditions. In another modification, an in. ductance I, Fig. 17, is connected in series with the regenerating armature A<1>, and the field F<1> is excited solely by the auxiliary generator 3. The motor 2 of the auxiliary set has a series field 5 and a shunt field 6, an adjustable resistance 7 being included in circuit with the latter. The generator has a series field coil F<g> and a field coil 10 which carries the current of the motor 2.